Field of the Invention
The present invention relates to optimizing mobile communications systems and, more specifically, to a method and system for designing cell sites.
Background of the Invention
FIG. 1 shows a block diagram of a conventional cellular radiotelephone communication system 5 which includes cells 6, radio base stations or cell sites 8, and a Mobile Telephone Switching Office (MTSO) or mobile switching center 9. As a mobile customer 7 moves from one cell to another a switch in the MTSO automatically switches connections with the respective radio base stations to maintain a continuous connection with the public switched network (not shown). Typically, a switch in an MTSO is connected to approximately one hundred cell sites.
In the past, radio base station antenna height and gain were chosen to realize a desired coverage area in a cell site. The overall reason for this was that the 3 Watt mobile phones did not have difficulty transmitting many miles to distant sites. Typically, if there was good downlink signal strength, the uplink was thought to take care of itself. (Downlink being defined as signals travelling from the cell site to the mobile unit and uplink being defined as signals travelling from the mobile unit to the cell site). The emphasis in designing cell sites was sending the signal out to the mobile phones in the downlink. The assumption has been that if the downlink was closed, the available uplink power would be sufficient to close the uplink in view of the high power mobile transmitters. Accordingly, cell site design calculations focus on the downlink characteristics and result in design parameters that consider only the downlink path. This downlink-focused view continues despite the decrease in maximum serving distance due to the transmitting power limitations of the new handheld portable phones.
The present invention is briefly described as a method of evaluating the coverage of a geographic area serviced by a communication system. The preferred embodiment discloses a method of selecting parameters in the design of a cell site in a wireless telecommunications system, including identifying a proposed location for the cell site; determining the maximum allowable loss to close the link between the cell site and a mobile unit in a cell, based at least in part on uplink propagation parameters; calculating the predicted loss based on a selected propagation model; and selecting operating parameters so that the predicted loss is less than the maximum allowable loss.